1. Field of the Invention
The present invention relates to an array antenna system and a transmit/receive module thereof for use as a radar apparatus and the like.
2. Description of the Related Art
An electronic scan-type array antenna system that has a plurality of two-dimensionally arrayed element antennas and that scans by changing a transmitting directivity of pulse signals transmitted from those element antennas and a receiving directivity of their reflected waves by way of phase control has been used as a radar apparatus and the like.
Among such array antenna system, there has been known an antenna system in which components that are connected to each element antenna and that perform the phase control of the transmitting/receiving signals are combined as a transmitting/receiving unit. A unitary unit is formed by units having transmitting and receiving paths connected to one element antenna through a circulator.
The unitary unit described above may be brought together with a plurality of element antennas and FIG. 1 shows a prior art exemplary structure in which a transmitting/receiving unit is formed by combining two unitary units for example.
Each of a plurality of, e.g., five, transmit/receive modules 31 is connected with element antennas 32a and 32b in the array antenna system 30.
The transmit/receive module 31 is composed of two unitary units 31a and 31b having the same structure from each other. The unitary unit 31a has a three-terminal circulator 41a having terminals A, B and C, a receiving amplifier 42a, a receiving phase shifter 43a, a transmitting phase shifter 44a and a transmitting amplifier 45a. A transmitting signal sent from a transmitting signal generating section 34 is distributed by a transmitting signal distributing section 33. Then, the transmitting phase shifter 44a applies a phase shift amount controlled by a transmitting/receiving phase control section 38 to the transmitting signal and the transmitting amplifier 45a amplifies it. The signal is then input to the three-terminal circulator 41a and is transmitted from the element antenna 32a. 
Reflected waves enter the element antenna 32a and after passing through the three-terminal circulator 41a, the receiving amplifier 42a and the receiving phase shifter 43a, are synthesized by a received signal synthesizing section 35. A received signal processing section 36 electrically conducts image processing on the synthesized signal and an image displaying section 37 displays a radar image. The same applies also to the unitary unit 31b. 
This prior art array antenna system 30 has had a problem that it requires the transmission phase shifters 44a and 44b and the transmission amplifiers 45a and 45b because it has the receiving and transmitting paths per each of the unitary units 31a and 31b. 
It is conceivable to form one of the unitary units, e.g., the unitary unit 31b, close to the both ends of the apparatus to have only the receiving path in order to reduce the transmission phase shifters 44a and 44b and the transmitting amplifiers 45a and 45b. However, if the antenna system is constructed as such, there have been problems that an apparent size as an antenna becomes small and an antenna gain drops, degrading in performance as an antenna system.
There has been also known an array antenna system having a transmit/receive module having a distributing synthesizer as disclosed in Japanese Patent Disclosure TOKUKAI No. Hei. 6-53726 for example (see FIG. 4 in particular). However, this is an antenna system having a pair of cross dipole antennas for polarized waves in X and Y directions and its purpose, construction and advantages are different from those of the present invention.